The present invention relates to a method and apparatus for selectively gripping and releasing objects. More particularly, the invention relates to an elastomeric gripping element mounted in a housing and configured to have an interference fit under normal conditions with the surface of the object to be gripped.
There are a number of devices used to grip shafts, pipes, and other objects, some of which have been in use for a number of years. Almost all of the gripping devices currently being used operate in an active manner. An xe2x80x9cactivexe2x80x9d operating device is one that is normally not in a gripping configuration, but must be selectively and actively forced into gripping an object. In contrast, xe2x80x9cpassivexe2x80x9d devices normally exist xe2x80x9cat restxe2x80x9d in a gripping mode. Such passive devices must be selectively operated to cause them to not grip an object.
Tubular collets or split rings which obtain their flexibility by provision of one or more slots in a metallic tube wall parallel to the tube axis and which change the gripping surface diameter by wedging on conical surfaces due to application of axial loads constitute a large, general class of gripping devices. Examples of this class of device are illustrated in several patents such as Knox U.S. Pat. No. 2,962,096; Richey U.S. Pat. No. 4,105,262; Russell U.S. Pat. No. 4,438,822; Reneau U.S. Pat. No. 4,728,125; and Nagano et al. West Germany Patent 24 39 100.
These collet or split ring devices are active devices, requiring the application of force to distort a normally nongripping element into a gripping configuration. Such devices normally have a very limited range of diameters which they can grip. When such devices are forced to distort too much they undergo permanent deformation. For example, collets can normally provide only limited gripping without being permanently distorted.
A similar class of active device uses a solid metallic ring or tube extension which fits very closely to the surface to be gripped and wedges conically tapered surfaces under the action of axial loads to effect gripping. The solid metallic ring is forced against the gripped surface by the wedging action. Such devices require a careful control of diameters of the gripping and gripped surfaces in order to avoid permanent distortions to the gripping ring. Examples of such devices are the Amlok devices, obtainable from Advanced Machine and Engineering, Rockford, Ill. and devices obtainable from Hxc3xa4nchen Hydraulic Gmbh, Ostfildem, Germany.
The Mapeco shaft coupling (Mapeco Products, Locust Valley, N.Y.) operates with the same type of solid ring gripping mechanism as the Amlok and Hxc3xa4nchen devices. However, the Mapeco device must be actively actuated by hydraulic pressure to grip.
Another class of gripping devices produces metal-to-metal gripping engagement for shafts by means of active hydraulically induced bulging of a gripping sleeve to cause it to distort into engagement with the gripped object. The Amlok hydraulic squeeze bushing (Advanced Machine and Engineering, Rockford, Ill.) requires active maintenance of hydraulic pressure in order to maintain its grip. The ETP bushing (Zero-Max/Helland Motion Control Products, Minneapolis, Minn.) uses a permanently entrapped somewhat compressible fluid to induce clamping. Yet the fluid must be constantly pressurized by a piston actuated by screws. Both types of bulging sleeve can operate only over very small gripping diameter ranges. Similarly, Amlok clamp disks and rings operate by selectably applied active direct compression of the gripped object, thereby permitting development of friction on the contact interface.
Non-split mechanical ring gripping devices may be actively forced under application of axial loads into gripping by flexurally deforming into contact with the gripped surface. Speith hydraulic actuated clamping sleeves (Advanced Machine and Engineering, Rockford, Ill.) uses a circumferentially convoluted sleeve for a flexural gripping device, whereas Russell (U.S. Pat. No. 4,438,822) uses an array of Belleville springs for gripping. Both types of device have only a very limited range of gripping diameters without undergoing permanent deformation.
A very common type of gripping device termed a xe2x80x98slipxe2x80x99 is based upon wedging of one or more discrete wedges of either planar or arcuate construction. Examples of such gripping devices can be obtained from Stewart and Stevenson, Houston, Tex. and Morgrip Products, Walsall, England. The wedges of these devices are normally actively biased into engagement with the gripped object by gravity or springs. Such slips are unidirectional gripping devices which will resist motion in the direction which tightens the wedge, but will release for motions which will loosen the wedge. Most slips have relatively steep wedge angles so that they are self-releasing when subjected to reversed axial loads. In addition, some slips come with separately operable release mechanisms which pull the wedges out of engagement. The Stewart and Stevenson slips for their conductor pipe connector are of a conventional construction, but are not readily releasable. Oilfield drill pipe slips are a more typical construction. The Morgrip Pipe Clamp uses wedged rolling balls as slips in a manner similar to a common type of one-way clutch. Slips are used to grip objects which have a relatively large size variation capability. One major disadvantage with many slips is induced damage to the gripped surface from teeth on the face of the slips or, for the Morgrip Pipe Clamp, from the balls.
Knox U.S. Pat. No. 2,962,096 and Russell U.S. Pat. No. 4,438,822 disclose rubber rings which are actively axially compressed to grip. The Knox rubber ring is intended to seal against a pipe, but in the process provides some level of gripping. Both devices function similarly to the expandable rubber bottle stoppers which are actively caused to expand to seal and grip by axial squeezing applied by a camming lever.
Nixon U.S. Pat. No. 4,121,675 works similarly to the Russell rubber gripper, but utilizes knitted metal instead of rubber. Rubber collets are commonly used in machine shops to grip drills or tool shanks. These devices use active axial compression of the rubber element against a cylindrical case with a self-releasing conically tapered back wall to cause the rubber to distort to induce gripping. Normally, radial steel inserts embedded in the rubber are used to grip the object, rather than using the rubber directly. Rubber collets accurately and effectively grip over a large diameter range.
Richey U.S. Pat. No. 4,131,167 discloses an active helical spring gripping mechanism which uses twisting of the spring to cause it to grip a cylinder. The gripping is through friction developed in a manner somewhat comparable to a wrap spring one-way clutch, but the spring ends must be actively held in a tightly wound condition to grip.
Russell U.S. Pat. No. 4,438,822 discloses the only known passive device. This Russell device has a passive torsional spring gripper which normally has an interference fit with the surface to be gripped. The spring is twisted to get it to release. Both this device and that of Richey can experience difficulty with the initial establishment of gripping due to buildup of friction not permitting full engagement with the gripped object over the full length of the helix. Additionally, both devices are sensitive to vibrations and are not well suited for axial load resistance.
Thus, a need exists for a passive preloading gripping device that does not rely on applying external mechanical force to efficiently initiate or maintain the gripping action on an object.
The invention contemplates a simple, inexpensive device for solving the problems and disadvantages of the prior approaches discussed above. The present invention provides a rapid, reliable and accurate gripping of objects without the application of an external mechanical force to efficiently initiate or maintain the gripping action on an object.
One aspect of the present invention is a gripping apparatus having a housing, an elastomeric gripping element anchored to one end of the housing, a reciprocable movable end attached to the gripping element, and a means for reciprocably moving the movable end between a first position and a second position, such that when the movable end is in the first position the gripping element is stretched and when the movable end is in the second position the gripping element is relaxed.
Another aspect of the present invention is a gripping device having an elastomeric gripping element securely attached to a static anchor end and a moveable end, where the movable end is moved in either direction with a hydraulically actuated piston.
Yet another aspect of the invention is a gripping apparatus having an elastomeric gripping assembly that has an elastomeric gripping element containing an embedded antiextrusion device, a static anchor end and a movable end. The movable end can be moved from its original position to stretch the elastomeric gripping element and can be returned to its original position to relax the gripping element and release the object being gripped.
Still yet another aspect of the invention is a process for gripping an object comprising the steps of: (a) selecting the object to be gripped by a gripping apparatus having a housing, an elastomeric gripping element anchored to one end of the housing, a reciprocable movable end attached to the gripping element, and a means for reciprocably moving the movable end between a first position and a second position, such that when the movable end is in the first position the gripping element is stretched and when the movable end is in the second position the gripping element is relaxed; (b) moving the movable end of the gripping apparatus to the first position to stretch the gripping element; (c) inserting the object to be gripped into the interior of the gripping apparatus; and (d) moving the movable end toward the second position to bias the gripping element against the object to be gripped.
The foregoing has outlined rather broadly several aspects of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed might be readily utilized as a basis for modifying or redesigning the structures for carrying out the same purposes as the invention. It should be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.